(1) Field of the Invention
The present invention is directed to a two-phase bang-bang current control synchronizer for use with a hysteresis controller including a power chopper. The two-phase bang-bang current control synchronizer synchronizes two current streams which pass through the controller. The synchronizer is used in connection with, for example, a solar inverter, to minimize the amount of current ripple which enters the inverter.
(2) Description of the Related Art
Prior art control systems for a power chopper require reference timing signals to initiate the start of a chopper cycle and turn the power chopper ON. The chopper is turned OFF by a demand signal which is indicative of how much current is necessary for the device to operate. Systems of this type do not require a control loop which has a bandwidth that is as high as a bang-bang controller because they use timing pulses for synchronization. A high bandwidth is necessary to provide a good dynamic response under transient conditions. These timing pulses provide a fixed timing reference voltage in a chopper but require additional circuitry to determine when to turn OFF the fixed timing reference pulses.
In locations in which there is no utility power, electricity is sometimes derived from solar power. Uninterruptible power supply systems have been used to convert the output from solar cells into usable energy. Uninterruptible power supplies, however, are not packaged for environments in which corrosive conditions such as pollution, humidity, heat, salt, air, and wind are present. These environments corrode the inverters and lead to failures. Using low and variable battery voltages in solar power systems overcome some of the drawbacks of the uninterruptible power supply but make direct inversion inefficient.
Hysteresis controllers have been used with a two-phase step-up chopper to control the chopper cycle. The step-up chopper improves the efficiency of the chopper and reduces peak current in the device. Hysteresis controllers have two threshold levels--an upper voltage threshold level and a lower voltage threshold level. An input current and a feedback current input to the hysteresis controller vary between the hysteresis controller levels where they reach, or "bang" against one threshold level, reverse direction until they reach or "bang" against the other threshold level and again reverse direction and repeat the cycle. With two phase chopper controllers employing this method, the input current and the feedback current tend to drift out of synchronization with each other due to slight variations in the circuit parameters.